24,095 research outputs found
Coherent phonon scattering effects on thermal transport in thin semiconductor nanowires
The thermal conductance by phonons of a quasi-one-dimensional solid with
isotope or defect scattering is studied using the Landauer formalism for
thermal transport. The conductance shows a crossover from localized to Ohmic
behavior, just as for electrons, but the nature of this crossover is modified
by delocalization of phonons at low frequency. A scalable numerical
transfer-matrix technique is developed and applied to model
quasi-one-dimensional systems in order to confirm simple analytic predictions.
We argue that existing thermal conductivity data on semiconductor nanowires,
showing an unexpected linear dependence, can be understood through a model that
combines incoherent surface scattering for short-wavelength phonons with nearly
ballistic long-wavelength phonons. It is also found that even when strong
phonon localization effects would be observed if defects are distributed
throughout the wire, localization effects are much weaker when defects are
localized at the boundary, as in current experiments.Comment: 13 page
The Físchlár digital video system: a digital library of broadcast TV programmes
Físchlár is a system for recording, indexing, browsing and playback of broadcast TV programmes which has been operational on our University campus for almost 18 months. In this paper we give a brief overview of how the system operates, how TV programmes are organised for browse/playback and a short report on the system usage by over 900 users in our University
Effect of Short Term Exercise and High Fat Diet on Skeletal Muscle miR133a
Micro RNAs (miR) are small non-coding RNA that regulate gene expression at the post-transcriptional level. miR133a is abundant in cardiac and skeletal muscle. In skeletal muscle, miR133a is best known for its regulatory role in myogenesis and differentiation. Nie (2016) found that muscle miR133a expression increased after acute exercise and with 12w of treadmill exercise training in mice. Knockdown of miR133a in transgenic mice resulted in blunted skeletal muscle mitochondrial biogenesis and function in response to exercise training (Nie, 2016) suggesting a role for miR133a in regulating the normal skeletal muscle metabolic adaptive response to exercise. Among other miR, skeletal muscle miR133a is reported as downregulated in insulin-resistant muscle. Insulin resistance in mice fed a high-fat diet is detectable after 3 days on diet (Lee, 2011). In this study, voluntary, rather than forced, exercise was employed to test whether miR133a expression is regulated early in the adoption of increased daily physical activity
High Abundance of Nesting Long-Eared Owls in North Dakota
The long-eared owl (Asio otus) is a secretive, poorly understood species in the Great Plains of the United States and Canada. In North Dakota the long-eared owl has been considered a species of special concern (Petersen 1991), due mainly to lack of information on its occurrence and nesting status. We discovered 39 long-eared owl nests while searching for Cooper\u27s hawk (Accipiter cooperii) nests in northwestern and north central North Dakota during April and May 2000. Long-eared owl nests mainly were observed at J. Clark Salyer and Des Lacs National Wildlife Refuges (NWRs) in the Souris River basin (for study area descriptions see Nenneman et al. 2002) and at Lostwood NWR on the Missouri Coteau landform (Murphy 1993). These 39 nests exceed the total of all state breeding records for the long-eared owl through the early 1970\u27s (Stewart 1975: 159). During 1994 to 1999 we annually found 2 to 12 long-eared owl nests while searching for Cooper\u27s hawk nests in approximately the same area of North Dakota
Minimal phrase composition revealed by intracranial recordings
The ability to comprehend phrases is an essential integrative property of the brain. Here we evaluate the neural processes that enable the transition from single word processing to a minimal compositional scheme. Previous research has reported conflicting timing effects of composition, and disagreement persists with respect to inferior frontal and posterior temporal contributions. To address these issues, 19 patients (10 male, 19 female) implanted with penetrating depth or surface subdural intracranial electrodes heard auditory recordings of adjective-noun, pseudoword-noun and adjective-pseudoword phrases and judged whether the phrase matched a picture. Stimulus-dependent alterations in broadband gamma activity, low frequency power and phase-locking values across the language-dominant left hemisphere were derived. This revealed a mosaic located on the lower bank of the posterior superior temporal sulcus (pSTS), in which closely neighboring cortical sites displayed exclusive sensitivity to either lexicality or phrase structure, but not both. Distinct timings were found for effects of phrase composition (210–300 ms) and pseudoword processing (approximately 300–700 ms), and these were localized to neighboring electrodes in pSTS. The pars triangularis and temporal pole encoded anticipation of composition in broadband low frequencies, and both regions exhibited greater functional connectivity with pSTS during phrase composition. Our results suggest that the pSTS is a highly specialized region comprised of sparsely interwoven heterogeneous constituents that encodes both lower and higher level linguistic features. This hub in pSTS for minimal phrase processing may form the neural basis for the human-specific computational capacity for forming hierarchically organized linguistic structures
Discovery of a Perseus-like cloud in the early Universe: HI-to-H2 transition, carbon monoxide and small dust grains at zabs=2.53 towards the quasar J0000+0048
We present the discovery of a molecular cloud at zabs=2.5255 along the line
of sight to the quasar J0000+0048. We perform a detailed analysis of the
absorption lines from ionic, neutral atomic and molecular species in different
excitation levels, as well as the broad-band dust extinction. We find that the
absorber classifies as a Damped Lyman-alpha system (DLA) with
logN(HI)(cm^-2)=20.8+/-0.1. The DLA has super-Solar metallicity with a
depletion pattern typical of cold gas and an overall molecular fraction ~50%.
This is the highest f-value observed to date in a high-z intervening system.
Most of the molecular hydrogen arises from a clearly identified narrow (b~0.7
km/s), cold component in which CO molecules are also found, with logN(CO)~15.
We study the chemical and physical conditions in the cold gas. We find that the
line of sight probes the gas deep after the HI-to-H2 transition in a ~4-5
pc-size cloud with volumic density nH~80 cm^-3 and temperature of only 50 K.
Our model suggests that the presence of small dust grains (down to about 0.001
{\mu}m) and high cosmic ray ionisation rate (zeta_H a few times 10^-15 s^-1)
are needed to explain the observed atomic and molecular abundances. The
presence of small grains is also in agreement with the observed steep
extinction curve that also features a 2175 A bump. The properties of this cloud
are very similar to what is seen in diffuse molecular regions of the nearby
Perseus complex. The high excitation temperature of CO rotational levels
towards J0000+0048 betrays however the higher temperature of the cosmic
microwave background. Using the derived physical conditions, we correct for a
small contribution (0.3 K) of collisional excitation and obtain TCMB(z =
2.53)~9.6 K, in perfect agreement with the predicted adiabatic cooling of the
Universe. [abridged]Comment: 24 pages, 24 figures, accepted for publication in A&
Strong Correlation to Weak Correlation Phase Transition in Bilayer Quantum Hall Systems
At small layer separations, the ground state of a nu=1 bilayer quantum Hall
system exhibits spontaneous interlayer phase coherence and has a
charged-excitation gap E_g. The evolution of this state with increasing layer
separation d has been a matter of controversy. In this letter we report on
small system exact diagonalization calculations which suggest that a single
phase transition, likely of first order, separates coherent incompressible (E_g
>0) states with strong interlayer correlations from incoherent compressible
states with weak interlayer correlations. We find a dependence of the phase
boundary on d and interlayer tunneling amplitude that is in very good agreement
with recent experiments.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. Let
- …